How do I modify a car's class and purchase cost?

[Madatek]

Believe it or not, I googled it and couldn't find any answer (just like for my life). I basically have a lot of mods installed and I wanted to create (only for myself, at least for now) a carreer mode, kinda like the one you would see on something like Gran Turismo, so get a car, race in championships, ???, profit.

So, what I want to do is kinda explained in the title of the thread - also I would need to mix up the mods, I believe.

Thanks for everyone who can help, or even took his/her time to read this. You made me happy. Have a smiling face.